1. Field of the Invention
The present invention relates to an auto choke apparatus that drives a choke valve of an intake system by using a bimetal.
2. Description of the Related Art
A choke valve is provided in a carburetor that is part of an intake system of an engine to improve starting performance. By closing the choke valve, an air fuel mixture can be made denser with a reduced amount of intake air so that the engine can be started smoothly. If the air fuel mixture is temporarily made denser by operating the choke valve in this manner, it is necessary to moving the choke valve back in the opening direction after the engine is started to maintain a good driving state of the engine by making the air fuel mixture thinner. To automate such a choke valve operation, an auto choke apparatus that operates the choke value by a bimetal is proposed (see, for example, Japanese Patent Application Laid-Open (JP-A) No. 4-262043). The auto choke apparatus drives the choke valve by a bimetal disposed near a muffler and the choke valve is moved back in the opening direction according to a rising muffler temperature after the engine is started.
In addition to the choke valve, a throttle valve to mainly adjust the amount of intake air is provided in the carburetor that is part of the intake system. Since the two valves are provided in the intake system for adjusting the amount of intake air, it is necessary to cause the choke valve and throttle valve to work together to adjust the density of the air fuel mixture appropriately. For example, if, immediately after the engine is started when the choke valve is operating in the closing direction, the throttle valve is operated in the closing direction, it is necessary to operate the choke valve in the opening direction in conjunction with the throttle valve so that the air fuel mixture is not made excessively dense. In an auto choke apparatus according to JP-A No. 4-262043, the throttle valve and the choke valve are caused to work together by transferring a rotational movement operation of a throttle lever fixed to the throttle valve to a choke lever fixed to the choke valve.
However, a bimetal is coupled to the choke valve and thus, when the throttle valve and the choke valve are caused to work together, it is important to configure the throttle valve and the choke valve in such a way that the operation of the throttle valve is not hindered by the bimetal. In the auto choke apparatus according to JP-A No. 4-262043, therefore, an arm member is provided freely rotatably with respect to the choke valve, and the choke valve and the bimetal are coupled via the arm member. Further, a choke lever is fixed to the choke valve. Thus, if the arm member is rotated to overtake the choke lever, the choke lever and the arm member rotate simultaneously. Accordingly, in a stage before the bimetal operates according to a rising muffler temperature, the choke lever can be moved rotationally without being hindered by the arm member (bimetal) so that the throttle valve and the choke valve can be caused to work together.
However, providing the arm member, in addition to the choke lever, for the choke valve leads to an increase in the number of components of an auto choke apparatus and also to a higher cost of the auto choke apparatus.
Moreover, placing the arm member between the choke valve and the bimetal leads to a higher cost of the bimetal. That is, since large allowance of the arm member is set between the choke valve and the bimetal, it is necessary to move the bimetal by a large operating angle to transmit the rotation operation of the bimetal to the choke valve. Thus, using the bimetal of a large operating angle leads to a higher cost of an auto choke apparatus.